1. Field of the Invention
The present invention relates to gauge systems for indicating the level of liquid in a tank and providing an alarm signal when a predetermined level has been reached.
2. Description of the Prior Art
U.S. Pat. No. 4,924,703, assigned to the assignee of this invention, discloses a prior art apparatus for indicating the level of liquid in a tank. The patented apparatus comprises a float encircling a guide tube extending down into the tank. The float is magnetically coupled to a gauging tube. As the liquid level rises, the float carries the gauging tube upwardly. The patented apparatus also has a mechanism for automatically visually and audibly alerting the tankerman when the level has reached a particular level, such as near full. This mechanism includes a reed switch mounted on the tank above the upper end of the guide tube and a level alarm magnet disposed within the gauging tube. The level alarm magnet comes into close proximity to the reed switch to actuate it as the tank is becoming filled.
While this system performs quite well, it does not adapt conveniently to different types of liquid ladings. More specifically, some tanks are used to carry a variety of products with varying densities and, in each such different liquid product, the float will submerge to a different level. Therefore, the liquid level at which the switch will be triggered will vary, since the triggering alarm magnet is at a fixed position in the gauging tube. Thus, to ensure accurate level indications for all liquids, there must be provided for each different liquid a different gauging tube with its alarm magnet fixed at a different position tailored for the particular liquid. This is inconvenient and expensive.
In the barge tank embodiment disclosed in the aforementioned patent, the magnetic coupling between the float and the gauging tube is provided by magnets carried by those parts in such position that they are magnetically coupled when the float and the gauging tube are both disposed in their lowermost positions. But in other applications, such as in railway tank cars, it is desirable to have the gauging tube coupling magnet disposed well below the float magnet when the two parts are both disposed in their lowermost positions, so that there is no magnetic coupling therebetween. Thus, the tankerman cannot be sure when the gauging tube and the float are magnetically coupled so as to know when to begin filling the tank.